1. Field of the Invention
This invention relates to improvements in a disc road wheel which is produced by press-fitting an outer peripheral section of a disc to an inner peripheral section of a rim and by welding them, and more particularly to such a disc road wheel in which a blow hole is effectively prevented from being formed in a welding bead (re-solidified) portion formed by the welding.
2. Description of the Prior Art
A conventional disc road wheel is usually formed by press-fitting the outer peripheral section of a disc to the inner peripheral section of a rim, and then by welding the disc outer peripheral section and the rim inner peripheral section along a peripheral direction, in which a welding bead (re-solidified linear deposit of molten metal) is formed along the periphery of the rim. This is, for example, disclosed in "Automotive Engineering Complete Book", Volume 19 ("Production Method of Automotive Vehicle"), published by Kabushiki-Kaisha Sankai-do, the first edition published on Apr. 20, 1980.
However, drawbacks have been encountered in the above conventional disc road wheel. That is, assume that welding of the rim and the disc is made by using a laser beam under a state in which remaining liquid materials such as machining oil and/or cleaning solvent exist between the disc and the rim. At this time, the remaining liquid materials such as machining oil and/or cleaning solvent are rapidly heated by the laser beam and promptly vaporized thereby developing a high internal pressure between the disc and the rim. This high internal pressure blows up molten metal during the welding so that drops of the molten metal are splashed. Accordingly, there is the possibility of blowholes being formed in the welding bead (re-solidified linear deposit of the molten metal) thereby causing welding defects.
Otherwise, in order to avoid the formation of blowholes in the welding bead, it may be proposed to remove the machining oil, cleaning solvent and/or the like existing on the surface of the disc and/or the rim at portions to be press-fitted to each other under rinsing, prior to the press-fitting of the disc to the rim. However, there arise difficulties in which a considerably high pressure is required during the press-fitting, and galling will be produced between the disc and the rim.